The invention relates generally to a method of fabricating a piezoelectric ceramic. More particularly, the present invention relates to a method of fabricating a piezoelectric ceramic having a small grain size and a fine grain pattern.
A piezoelectric ceramics is usually used in an ultrasonic transmit/receive device, an ultrasonic wave transducer for non-destructive, a fish finder, an optical set, an optical modulator color filter, an actuator for controlling combustible gases, a special use piezoelectric devices, etc.
Conventionally, as a method of mixing the PZT power being a raw materials of a piezoelectric ceramics, a solid phase reactive method is usually employed by which major components of PbO, ZrO2 and TiO2 and the impurity material of Nb2O5, etc are mixed and are then calcined. Recently, however, a composite powder method including a chemical method such as alcoholcide method, coprecipitation method, a multi-step wet method, etc. is attempted.
The composite powder obtained by chemical method is extremely fine and can maintain its grain pattern intact because it does not experience a mixing crushing process. Thus, as intrusion of the impurity can be prevented, the chemical method has a superior characteristic to a calcination powder obtained by the conventional solid phase reactive method. However, in manufacturing the PZT ceramics, the solid phase reactive method has been still mainly employed but the chemical method has not been practical. The reason is that if the PZT is combined by the chemical method, the manufacturing process is complex and the product cost is high.
Meanwhile, with crushing technology advanced, the powder combined by the conventional method is crushed into up to sub-micron. This crushing technology is a lot employed to fabricate various types of ceramics in view of a low temperature sintering.
As mentioned above, a method of making a fine powders and sintering it at low temperature can be mainly classified into a method of combining a powder body using a chemical method and a method of combining the powder body by solid phase reactive method using the material mechanically finely crushed. Any of these methods has their purpose to miniaturize the grain of the powder and increase uniformity of the composition, thus improving the electrical characteristic even at low temperature.
FIG. 1 is a flowchart for explaining the conventional method of fabricating the piezoelectric ceramics.
Referring now to FIG. 1, the major components, ZrO2 and TiO, and an inpurity, Nb2O5 are first weighed depending on a (Zr0.53Ti0.47)Nb0.0102 oquation and mixed by ball mill for 6 hours (S101). Then, a first calcinations process is performed at the temperature of 1400xc2x0 C. for 6 hours to make a NZTO solid solution powder (S102 and S103). In order to make this NZTO powder much fine, it is finely crushed by a 2.5 zirconium ball for 12 hours. Then, in order to satisfy the following [Chemical Equation 1], PbO is added to the NZTO powder thus fabricated. After it is combined by ball mill for 6 hours (S104), a first dry process is performed (S105).
xe2x80x83Pb1.01(Zr0.53Ti0.47)O3+0.5 mol % Nb2O5xe2x80x83xe2x80x83(Chem Eq. 1)
Next, a second calcinations process is performed at the temperature of 710xc2x0 C. for 3 hours (S106). Then, after it is crushed (S107), a second dry process is performed (S108). After PVA is added as a binder (S109), it is finally granulated (S110). Then, this granulated powder is weighed to fabricate a cylinder shape sample (S111). After a sintering process is performed (S112), the characteristic of the fabricated sample is measured (S113).
Referring to FIG. 2, it can be seen that the calcination temperature must be more than 900xc2x0 C. in order to form a single phase.
However, the PZT powder of a piezoelectric ceramics fabricated by the above mentioned conventional method could not maintain its grain phase intact due to combined crushed process and has the possibility of introducing impurities. Also, there are problems that it requires a higher temperature in order to form a single phase and also needs a lot of processes.
It is therefore an object of the present invention to provide a method of fabricating a piezoelectric ceramics having a small grain size and a fine grain pattern by preventing intrusion of impurities upon manufacture of a piezoelectric ceramics.
In order to accomplish the above object, a method of fabricating a piezoelectric ceramics according to the present invention is characterized in that it comprises the steps of forming a combined powder being major components, stirring the combined powder with (COOH)2 water solution, dropping a Pb(NO3)2 water solution into the stirred powder, and forming a PZT powder by calcinations and sintering processes.